Television pickup tube system



Mmhn, 195s P. K wElMER TELEVISION PICKUP TUBE SYSTEM 2 sheets-shea 1v Filed June 5, 1951 wf: :um

INVENroR Pall] Weimer gigi/L March 1l, 1958 P. K. wElMER TELEVISION PICKUP TUBE SYSTEM 2 Sheets-Sheet 2 Filed. June 5, 1951 i NNN bx v MSN Q RW.

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iba I KALWNTOR imei' United fates y .Y 2,826,632 f TELEVISION PICKUP TUBE. SYSTEM Paul K. Weimar, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June s, 1951, seal No. 229,939

11 Claims. t (C1. 17ss.4)

The' present 'invention relates to television pickup tubes and, more particularly, to television camera tubes utilizing an image section. l

'Television camera tubes using an image section have been described in an article by Albert Rose, Paul K. We'imerv (the present applicant) and Harold B. Law published inthe Iulyvl946 issue of the Journal of the InstituteA Aof iRadio Engineers, Vpages 424432. In such tubes' an` optical image is projected upon a photocathode spaced from vone side of a semi-conductive target lm. A` charge pattern, correspondingto the optical image, is produced Ion thesurface of the semi-conductvetarget film by elecl-trons emitted from the photocathode. An electron beam iis scannedover the opposite surface of the target lm :and discharges the charge pattern by losing electrons 'thereto in proportion to the amount of charge at each ele- ;mental area. /This loss of electrons modulates the beam which is directed onto a collector to provide the output rsignal.

An object ofthe present invention is to provide imjproved means for reading the charge pattern on the target of a tube of the character described whereby background :noises will be substantially eliminated.` 'Another object ofthe invention is to devise a pickup #tube using light spot scanning.

Another object of the invention is to devise a pickup tube having a low Velocity image section.

atent nected thereto are mesh screens 14 and 17. A pair of' mesh screen electrodes and 16 are respectively closely mounted on opposite sides of target lm 13. The side of the target averted from the photocathode 12.bears an: electron-emissive `layer 19 and faces a collector comprising an electronmultiplier havingan output collecting electrode' 26. ElementZl'of multiplier 20 is a solid Y dynodeelectrodelocated behind an aperture 27 of the collector wall. Elements'22, 23 and 24 are pinwheel type multiplier sections having dynode vanes inclined to the axis of the multiplier, the vanes of alternate sections being inclined in opposite directions. The last multiplier stageris a solid dynode electrode from which secondary electrons are directed `to and collected by electrode 26.

Still another object of this invention is to provide means for increasing the sharpness of definition of the charge pattern in a'pickup tube having a low velocity image section and for preventing premature obliteration thereof due to theipassage of electrons from more negative to more positive portions of the pattern.

A further object of the invention is to provide means for adapting a tube of this .character for multiple pickup, whereby a plurality of outputs corresponding, for example,V to the three primary color components may be 11`ig..3 is ak section through the tube of Fig. 2 taken on :the line 3-3.

tube

generally designated 10 and comprising a glass tubular envelope 11. A. photocathode 12 is formed on anl :innerend Wall of the envelope. A partially conductive glass lm 13v is mounted parallel to the photocathode 12 :andjsp'acedbetween the ends of envelope 11. An acceler- :at-ng-ele'ctrode 31s formed as a wall coating between.A gphotocathodelZ and target film, 13. Mounted respecr- Referring rst to Fig. V1, there is shown a camera pickup tively 'atfthe ends of"electrode 31 and electrically con- The multiplier'sectionV is of the type set forth in applicants Patent 2,433,941 issued January 6, 1948.

Electrodes 21i26 of the multiplier 20 are connected to points oi progressively higher positive potential on a voltage fdivjdern 28, bridged across a battery 29, to the grounded negative end o f which is connected the photocathode 12. Screens 14-18 alsoderive their potentials from this divider, so that screens 15 and 16 are slightly and screens 14, 17 and 18 are considerably more positive than photocathode 12; Y It will be noted that the first mulmultiplier section 21 is'held at the same potential as these latter screens, and is connected through the housing of the multiplier "20 which is inV contact with an accelerating electrode 30 formed as a conductive coating on the inner surface of envelope 11 and between the target'tilm 11 and the multiplier 21; Target 13 is not connected' ot any voltage source, its oating potential being determined (at 1 least Ain the absence of asignal) by that of the adjacent screens 15 and 16.

Ina practical embodiment the potentials used were as follows i Screens 15 and 16: :5 to 15 volts (positive with respect i to cathode 12) e Screens 14, 17, 18, and multiplier stage 21: 200 volts Multiplier stage 22: 600 volts p Multiplier stage 23: 900 volts Multiplier stage 24: 1200 volts Multiplier stage 25: 1500 volts Output electrode 26: 1600 volts A focusing coil 32, energized lfrom any suitable source of direct current (not shown), surrounds the envelope 11 and sets up a constant, axially directed magnetic field therein. A pair of horizontal deflecting coils and a pair of vertical dellecting coils are represented by one of each pair respectively shown at 33 and 34. These pairs of coils are respectively connected with corresponding pairs of coils of cathode ray tube 37 and represented byV one of each pair, respectively shown at 35 and 36. The coils are energized from respective deflection control circuits 38 and 39. The cathode ray tube 37 produces a luminous spot `on its screenft, which is focused upon the emissive coating 19 of target 13 by optical means, here illustrated schematically as a lens 41. Screen 40 is made of a fluorj escent material 'having a very short l afterglow, such as zinc oxide, tocause the spot thereon to be sharply dened during Vits displacement by the scanning coils 35, 36.

A suitable projection system, shown schematically as a lens 42, projects the image of a scene or object 43 upon j the photocathode 12.

Coils 33, 34 are so and released by light from the spot of tube 37, into the mouth 27 of the multiplier 20. This effect being subsequently referred to as descanning Target 13 may eonsist of very thin` glass of low resis- Y tiv1ty,'e. g. as described in U. S. Patent No. 27,473,220 'issued June 14, 1949,' to Albert Rose. In general this v Patented Mar. 11, s

` I dimensioned and connected to the coils 35, 36 as to deflect the photoemission from film 19 charges on opposite 'side'svof thetargt to occur within'the' period of one scanning frame,.`V thus in less than, say lo example, from `fivelto .ten timesthe vilan len lightf 'l When an imageof l.the ,object43 isproieeted upon the s photocathode 12 by the lens 42,521 corresponding electron' image is produced withinthe irnagefsection''ofthel tube4 between `cathode 12=and target 13. The electrons in`this`l section, after emanating from the photo'cathode, are ac? celeratedby the potential difference existing lbetween the cat hodeand. the Vfirst .sreen 14. `The electrons thereafter.

proceed atconstant speed, in thelield-free space bounded(15 by, the, screens 14Land 1.7,v andfbyl the wal1 electrode 31.y Afterpassingthroughscreen 15, theyelectrons are decelerateclvk by. the. braking, action of thevvmaterially lowerr second. A suitable thickncspf theglass mayv be,1 formA nlm. 19 bythe lens 41, scans aparticular, surface element Y of. theV emissive layer.19, the number of photoelectrons Y emitted by this surface element, which are transmitted bythe screen 16 will dependupon the magnitude ofthe negative. chargeY opposite this element on thecathode side ofthe target.

The brightest parts of the picture correspond to the areas of the targetV most negative with regard to the screen 16 and in these areas the photoelectrons excited by the scanning spot can most readily penetrate the screen. On the dark portion of the target the photoelectrons excited by the spot cannot pass the screen line. 'Ihe photoelectrons passing the screen 16 will be accelerated by the potential gradient between the screens 16 and 18 and v vill be focused by the magnetic lield of the coil 32 to form a be`am'44 directed substantially perpendicularly to the surface of the target 13; On entering the field of the descanning coils 33, 34 this beam will be deliected toward thernultiplier 20 which it enters substantially in axial direction, owing to theN termination of the descanning elld short of the mouth aperture 27.

'Ihelp'riniary'electrons'strike the Vfirst dynode ZIivvher'e Y' they give riseto a con `liable secondary emission; and

the bulk of pour th'pfimar'y and the'seeondry'elemens are thereupon v'a'.,ttracted't'tnlvard the successive stages 22, 23, and 24, liberating secondary 'electrons at each stage and finally reaching the collector electrode 26. 'The 'output signal is amaximum in the light and substantially zero in lthe dark.` In seine pickup tubes such as the image orthic'on the output ha'sth Opposite polarity whichifs undesirable because it permits spurious beam noise to degrade the dark areasy ofthe picture.

To reduce the accuracy' of synchronization required between the scanning'elments 35, z36 and the descanning elements 33, 34, the mouth aperture 27 of the collector 20 may ,be made considerably larger than the cross section of the beam 44'without risking the introduction of objectionable noise.y This is possible because most of the stray electrons appearing within the scanning section of the tube 10, e.' g'. electrons due to spurious photoexcitation of the layer 12, will generally not be deflected int' e multiplier .2Q but will Strike ether Surfaces Within the" tubs# Spud-@vs Phatcmission fram .the layer 19 may, ofcourse, be partly suppressed yby Yr'nalr'ing the body ning means 3 3, 3

ll also vser'ye'ftf'oreduce the chance the average outputvoltage andthe degree of its v-modulav tion will be substantially independent of the distance between the collector mouth 27 and theimage portion being scanned; in other words, the transmitted picture will be uniformly shaded.

If the screen 18 were omitted,` electrons designed to form the beam 44 might leave' the emissive layer 19 with an appreciable radial velocitycomp'onent, which would make focusing more difficult.

AnY important advantage derived from the use of the screens 14 and 17 in the image sectionofthetuberesides in the maintenance ofV a highdegree of resolution in the electron image and in the charge pattern of the target. Thus the steep potential'gradient adjacent the photocathode 12 will impart to the emitted electrons a large axial speed component so as to override their tendencies to move laterally from paths of great current density tofadjface'ntl paths of lesser densityf Also, secondary lec-A tronsreleased lat the target 13 (as well'as"primary"elec-l tronslwhich fail to reach the target) passn back toward the photocathode 12, by virtue of the accelerating ield betweenwthe screens 15 and 17, so Ias to bepreventd frgrn settlingdon themore; positive portions of the target. Sine hhesejrepell'ed Velectrons will have to' pass four times through a highlyA positive screen `(twice'th'roug'h` screen 17 and twice through screen 14) beforeagain Yapproaching the target, the probability of their absorp- Fig. 1. Wall electrode covers an'annular zone 130' ofi the scanning end of the tube 111. f

In contact with the conductive lining 130 and spaced uniformly about the window 111 areY three mutiplier sections 120a, 120bA and 120e, each representing an electron'multiplier preferably of the pinwheel type VVas more fully illustrated infFig. `1. Facing these multipliersV 120a; 120b and"12(l)'c arethree emissive layers 119a, 119b and 119e, respectively, provided 'on the scanned' side of the target 113. Three filters 15011, 150b and 150e arefposi-4 tioned outsidejthe envelope 111 adjacent the image end thereof andare respectivelyY aligned'with the layers 119e, 11912 and 119e` as Well'as'with lenses 142a, 142b, 142e interposed between tleseiltersand the object 143. The lenses, which are thus arrayed in a circle in exactly the manner shown more clearlyv .in Fig. 3Vfor thefcollectors 120e, 1 2Qb and 120e, receive''light fronfth object 143 by n'Way "f a"'thrjeesided prism "1,51 *and Vthree` 'suitably inclnedrriiorrs 152vz,1'52b`a`n'd152e.V 5"

On the scanning side the luminous spot on the screen v of "t`1be"137'l is `reproduce"d'mon the three layers 1191'1, 1191; and 1196 by alree-sidedprism 153 and a system of mirrors ISZtiz, 154bf154ic'and lenses 141j141ljf141'c generally similar to the system just described. It willv be notedfhoweve'i' thatthe fenses'ltd'lillb, 141e are inclined toward the tube axis yso thattheir rays'int'ersect within'the envelope 111; "after" traversing the window' 111", thereof. 'TWhere'thefsfe rays strike" the "target 113, they give rise toi-respective 'electron "beams 144a, 144b and 14.4@ which era'frste toward th mouth apertures-"bf the collectors lltlqflZrtlb and@120c'bytheidescanning 111, leaving aV window aaaaosa deection elements to descan all three beams 144a, 144b and 144e in the proper manner, it is only necessary that the relative positions between the simultaneously scanned target lareas and the corresponding mouth apertures be the same for all three collectors; as shown, this, may be accomplished by placing the three collectors opposite vthe respective Centers of the associated emissive layers 119a, 1`1`9b and 119e. Y- A Y y ^In the arrangement shown the collector 120a,valigned with the green filter 150a, produces an output `varying with the green color component of the image; similarly, the collectors 120k and 120e, aligned with red lter 150b and blue filter 150e, produce outputs'respectively varying with the red and the blue color component.

Although certain embodiments of the invention have been particularly described and illustrated by way of example, it should be understood that the same may be modied in various ways without thereby exceeding the scope of the invention as defined in the object and in the appended claims.

What is claimed is:

l. A television pickup tube comprising, an envelope, a photoemissive electrode adjacent to one end of said envelope, a target electrode spaced from said photoemissive electrode within said envelope, a pair of spaced screen electrodes positioned adjacent to said target electrode and between said target electrode and said photoemissive electrode, said screen electrodes being adapted to have different potentials applied thereto with said screen electrode closest to said target being adapted to have a negative potential thereon relative to the potential of said other screen electrode.

2. A television pickup device comprising an image section, a scanning section, an electron-permeable target separating said sections, a photoemissive element in said image section spaced from said target, electron-accelerating means adjacent said element, electron-decelerating means next to and between said electron-accelerating means and said target, the last-mentioned means producf ing a retarding lield suiciently strong to make the ratio of secondary emission at said target less than unity whereby a negative charge pattern is produced on said target by electrons arriving from said photoemissive element, an electron-emissive layer on the side of said target facing said scanning section, and reading means including said scanning section adapted to translate said charge pattern into a modulated output voltage.

3. A television pickup device comprising a photoemissive target, electronic means adapted to produce a charge pattern on one surface of said target, a source of light, optical means for focusing light from said source in a concentrated spot upon said target surface, scanning means for displacing said spot over said target surface for causing the emission of electrons'varying in quantity with said charge pattern, electronic focusing means for forming said electron emission into a beam, collector means spaced from said target, and beam deecting means synchronized with said scanning means for continuously directing said beam toward said collector means.

4. The combination according to claim 3 wherein said collector means comprises an electron multiplier having a mouth aperture which is large with respect to said spot fbut small with respect to said target.

5. The combination according to claim 3 wherein saidV source of light comprises a cathode-ray tube including a uorescent screen, said spot displacing means including a iirst set of deflecting elements associated with said cathaxially directed magnetic eld in a zone extending be-` tween said target and said 'collector means, said deecting means including a plurality of coils for producing a de'- scanning field in said zone betwee'nsaid target and said collector means.

7. A television pickup device comprising a photoemissive target and electronic means adapted to produce a charge pattern on said'tar'get, a source of light, optical means for focusing light from said source in a plurality of concentrated spots upon said target, scanning means for synchronously displacing said spots, .thereby causing the emission of electrons varying in quantity with said chargeqpattern, electronicfocusing means forV forming said electrons into a plurality of beams originating at the locations of said spots, respectively, a plurality of collectors spaced from said target, and deflectiug means synchronized with said scanning means for continuously directing said beams toward respective ones of said collectors.

8. A television pickup system comprising a tube having an image section and a scanning section, an electronpermeable target separating said sections, a photocathode in said image section spaced from said target, optical projection means for projecting a plurality of images of a given object upon said photocathode, said projection means including filter means for making said images representative of different color components, electrode Vmeans in said image section directing electrons from said photocathode onto said target, thereby producing a plurality of charge patterns on different portions of said target each corresponding to a respective one of said images, each of said target portions bearing a photoemissive layer on its side facing said scanning section, a source of light, optical means for focusing light from said source in a plurality of concentrated spots upon the photoemissive layer of each of said portions, respectively, scanning means for synchronously displacing said spots, thereby causing the emission of electrons varying in quantity with the respective charge patterns, electronic focusing means for forming said electrons so emitted into a plurality of beams each originating at a respective one of said portions, a plurality of collectors spaced from said target, deectng means synchronized with said scanning means and common to all of said beams for continuously directing said beams toward respective ones of said collectors, and a plurality of output means respectively connected to said collectors to produce output signals representing said color components.

9. An electron discharge device comprising, an envelope, a target electrode within said envelope and including a film of glass and a photoemissive coating on one surface of said glass tilm, means within said envelope for producing a charge pattern on the other surface of said glass film, an electrode spaced from said photoemissive surface for collecting electrons photoelectrically released from said coating, and deflecting means for directing said photoelectrons toward said collector electrode.

l0. An electron discharge device comprising, an en velope, a target electrode within said envelope including a film of glass and a photoemissive coating on one surface of said glass film, means within said envelope for producing a charge pattern on the other surface of said glass hn, said means including a photocathode spaced from said target and one electrode between said photocathode and said target for directing photoelectrons from said photocathode onto said other target surface, and an electrode spaced from said one surface of said target for collecting electrons photoelectrically released from said coating.

ll. An electron discharge device comprising, an envelope, a target electrode within said envelope and including a lm of glass and a photoemissive coating on one surface of said glass film, a source of light, and means for scanning said light as a spot over said photoemissive target coating, an electrode spaced from said target for Referenescifedin me mefcf'this' `patent UNITED; STATES lPATENTS 2,150,159 Gray Mar; 14,- 1939 :2,213,547 1amS. sept. 3, 1940 10 2,213,548 rams r v f r sept. 3, 1940 2,219,113 Prke 01:11.22, 1940 8y y Morton Y..- Aug. 5, 1941 VMierlo1 Sept, 16,1941 Farnsworth 1 Oct.. 7, 1941 YWilson Sept. 1, 1942 Morton Feb. 13, 1951v Weimer Mar. 20, 1950 Schroeder Mar, 20, 1951 Weimer- Mar. 20, 1951 Oliver Jan. 1, 1952 Rose- Feb. 19, 1952 vRose Nov. 18, 1952' McGee Sept. 15, 1953 

